At work yesterday, I was configuring a proxy server for a new company web site. For reasons beyond my control, it is running on port 87 instead of port 80, so the URL looks like http://somewhere.example.com:87/. When you try and load the site in Firefox 3, you get this friendly message:

If you can’t see the screenshot, it says: “This address uses a network port which is normally used for purposes other than Web browsing. Firefox has canceled the request for your protection.” They then offer you the utterly useless Retry button. What is going to change when you click Retry? Instead, there ought to be a way that lets you say “I really do understand that, let me do this anyway”. But there is nothing availabe here or in Tools->Options that lets you work around this behavior. Fortunately, there is a solution in about:config.

This is a special “page” built in to Firefox; enter about:config in the address bar. If you’ve never been here before, you will get a warning; you may want to uncheck the Show this warning next time before you click I’ll be careful, I promise!! button. Now right-click anywhere in the lower portion of the resulting page and select New and then String from the context menu. The name you need to enter is network.security.ports.banned.override, and the value is the port(s) you want to open. If you have more than one, enter them as a comma-separated list. That’s it, no need to restart your browser or do anything else, it should just work now.

Apparently, port 87 has had security exploits in the past, so the Mozilla folks really are trying to protect us. And also from what I read, this same restriction was in Firefox 2 and perhaps earlier versions. Since I no longer have FF2 available on any of my computers, I cannot confirm that. Mozilla developers: can’t we put things like this in some kind of GUI option so we can find stuff without endless Google searching? Thanks.